The present invention relates generally to an imaging module and an imaging reader for, and a method of, illuminating and imaging targets to be read over an extended range of working distances.
Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbol targets, and/or non-symbol targets, such as documents. A handheld imaging reader includes a housing having a handle held by an operator, and an imaging module, also known as a scan engine, supported by the housing and aimed by the operator at a target during reading. The imaging module includes an imaging assembly having a solid-state imager or imaging sensor with an array of photocells or light sensors, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged, and for projecting the return light onto the array to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electronic signals corresponding to a one- or two-dimensional array of pixel data over the imaging field of view. In order to increase the amount of the return light captured by the array, for example, in dimly lit environments, the imaging module generally also includes an illuminating light assembly for illuminating the target with illumination light in an illumination pattern for reflection and scattering from the target.
In some applications, for example, in warehouses having targets on products located on high shelves, it is necessary that such targets be capable of being read by the reader at an extended range of working distances, for example, on the order of thirty to fifty feet, away from the reader. For this purpose, it is known to employ two imagers: a so-called near imager or camera to image close-in targets over a relatively wide imaging field of view, and a so-called far imager or camera to image far-out targets over a relatively narrow imaging field of view. It is also known to employ two illuminating light assemblies, each customized for each imager. For example, the illuminating light assembly for the far-out targets generally illuminates such far-out targets with more intense, brighter illumination light as compared to the illuminating light assembly for the close-in targets. It is further known to employ zoom-type or liquid crystal-based illumination mechanisms to sequentially illuminate targets at different working distances from the reader.
Although generally satisfactory for its intended purpose, the known use of two imagers and two illuminating light assemblies, as well as the known use of zoom-type or liquid crystal-based illumination mechanisms, increases the size, cost, electrical power consumption, and complexity of the imaging module, and, in turn, of the overall reader. Sequential switching between illuminating light assemblies, and zooming between working distances, can cause the illumination patterns to appear to flicker and can, in some cases, annoy the operators of the readers, as well as bother nearby bystanders or consumers. Zoom response times can be slow. Any mechanical zoom part is subject to wear and tear and can produce undesirable noise. Stray illumination light from the illuminating light assemblies may, sometimes, interfere with the operation of the imaging assembly, which can cause reading performance to deteriorate.
Accordingly, there is a need to reduce the size, cost, electrical power consumption, and complexity of the imaging module and of the overall reader, to avoid flickering illumination light patterns, to improve response times, to avoid wear and tear from moving parts, and to prevent stray illumination light from degrading reading performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.